The disclosure relates to a method for controlling printing elements of an ink print head in a printing operation of an ink printing apparatus.
Ink printing apparatuses may be used for single-color or multicolor printing to a recording medium. The design of such an ink printing apparatus are described in DE 10 2014 106 424 A1 (U.S. Pat. No. 9,302,474 B2), for example. Such an ink printing apparatus has at least one print group having at least one print bar per print color. The print bar is arranged transversal to the transport direction of the recording medium and may have multiple print heads that possess a plurality of printing elements with nozzles in order to eject ink droplets from the nozzles. Each dot of a print line transversal to the printing direction is respectively printed by a different nozzle. The recording medium moves relative to the print bar. The nozzles thus print ink droplets in chronological succession in the longitudinal direction onto the recording medium. The higher the print resolution transversal to the transport direction of the recording medium, the more nozzles that are arranged in the print bars or the print head, or the closer (transversal to the transport direction) that the nozzles are arranged relative to one another.
During printing operation, the viscosity of the ink within a nozzle may not rise too severely, since otherwise there is the danger of the ink drying at the surface or drying out, such that the nozzle at least partially clogs and therefore an ink droplet may no longer be cleanly ejected, and/or its desired ejection direction is altered due to obstructing ink residues, such that the ink droplets are printed at a pixel or printing position that deviates from the desired position.
If the ink printing apparatus is in normal printing operation, an ink droplet is ejected again and again from the nozzles. As a result of this, the ink in the ink chamber and the nozzle channel refreshes. The danger of drying up is low in this state.
In a method for controlling vibrations in printing operation of the ink printing apparatus, multiple vibration cycles are inserted between two ejected ink droplets in the event that no ink droplets have been ejected from a nozzle for the length of a specific duration. The information about the activities and inactivity of nozzles are known from the print data that are supplied by the controller to the printer control.
During a vibration cycle, the actuator is activated with a predetermined waveform so that the ink meniscus at the output of the nozzle is set into vibration without ejecting an ink droplet. Via the vibration, the ink at the end of the nozzle channel is mixed so that ink with higher viscosity (having contact with the air) is mixed with fresh ink of lower viscosity from the ink chamber or the inside of the nozzle channel. In comparison to continuous printing without vibrations, the viscosity thus does not increase as quickly, and the danger of a clogging of the nozzle beginning is reduced.
In multiple ink printing apparatuses (DE 10 2014 101 428 A1=U.S. Pat. No. 9,205,645 B2, DE 10 2012 110 187 A1=U.S. Pat. No. 9,120,306 B2, and DE 10 2012 107 775 A1=U.S. Pat. No. 9,044,937 B2), meniscus vibrations are implemented depending on the size of the ejected ink droplets, depending on the velocity in delay ramps or acceleration ramps in the printing, depending on the printing pause etc. It is common to these ink printing apparatuses that multiple vibration cycles are performed in succession. The beginning of the first vibration cycle is established by the duration since ink droplets are no longer ejected from a nozzle. A constant number of vibration cycles is conventionally implemented. However, it may occur that, for some inks, the number of vibration cycles is too high, whereby a leaking of ink onto the nozzle plate can be observed.
For other inks (inks with different chemical/physical properties), the predetermined number of vibration cycles may be too low, such that the refresh effect is not sufficient and drying-out effects may occur, which is noticeable in the print image as what is known as a “first line effect” (meaning that dots printed with the first print line have a somewhat different appearance than the subsequent dots). Given use of various inks with different drying behavior, problems with degraded viscosity definitely may occur in the nozzles channels given one or another ink.
A method for controlling printing elements of an ink print head to eject ink droplets is described in U.S. Pat. No. 6,471,316 B1. This method is based on the object to control a print head such that the activation duration is as short as possible, which should lead to an increase in the print speed. For this, a “drive signal” and a “preliminary drive signal” are controlled, matched to one another, so that the droplet generation may already be started if the ink meniscus is still settling. The phases of the oscillation that were generated by the “drive signal” or the “preliminary drive signal” thereby must be generated in a predetermined phase position relative to one another so that the still-existent and decaying vibration does not interfere with the generation of the ink droplet; rather, the decaying oscillation is “in phase” with the next oscillation to generate an ink droplet. The two signals should be matched to one another. For this, a vibration status of the decaying oscillation is determined.
The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. Elements, features and components that are identical, functionally identical and have the same effect are—insofar as is not stated otherwise—respectively provided with the same reference character.